Experiments have been carried out on long, smooth, circular cylinders to establish accurate data on the fluctuating pressure distributions and r.m.s. lift and drag forces in sub-critical flow (104 <R< 2·5 × 105), on an elemental slice of the cylinder. Results of parametric studies of the effects of variation of Reynolds number, aspect ratio, turbulence of the incident flow and wind tunnel blockage are presented. Many other results have been published on this topic since 1950, but wide variations exist between them; the work reported here was undertaken to produce reliable data for its own sake and to provide the basis for a study of spanwise effects.